Vertical turbine pumps for deep water wells are well known and have been applied thoroughly in conventional pumping systems. FIG. 1 shows a typical prior art turbine driven deep water well pumping installation. The installation comprises an elongated cylindrical hole 2 extending from an open end at the surface 3 down into the ground 4, terminating at a closed end 5. The well penetrates the natural water table or phreatic level 6 of at least one aquiferous geological formation. A tubular casing 7 is inserted into the well to define a pumping chamber 8 and to prevent the well wall 9 from collapsing. The casing is made of steel, fiberglass, plastic such as polyvinyl chloride (PVC), polyethylene, or acrylonitrile butadiene styrene (ABS), or some other strong durable material. The casing is generally perforated from the phreatic level down to the well bottom to allow passage of water through to the inside of the casing. Gravel 10 is poured to fill in the annular gap between the well wall 9 and the casing 7. The gravel acts as a filter to prevent granular materials existing in the surrounding geologic strata from entering the casing. Naturally, the gravel is coarser than the perforations through the casing. A tube or pump column 11 through which water will be pumped out is inserted into the casing and extended down a distance beyond the phreatic level.
Typically, a deep water well pumping installation employs a turbine pump to extract the water from within the well. The turbine pump includes a motor 12 which is usually situated above ground. The motor drives a long drive shaft 13 which extends down through the tube, typically terminating a distance below the phreatic level with a set of bowls and impellers 15. Many impeller designs are available. Usually, the shaft is rotatively secured by one or more bearings 16 positioned within the tube made of materials such as rubber or bronze. These structures are also referred to as spiders or bushings. The pump can be lubricated by water or oil. A typical speed for the impellers is around 1800 rpm. The bottom of the tube 11 terminates just above the set of impeller bowls which are located between the bottom end of the pump column and the intake or suction port 17.
During pumping, the spinning impellers force water up the tube and out through a discharge head pipe 18. Water is drawn from the aquifer. Water existing in the surrounding formation can be said to converge toward the intake port through a series of successively smaller concentric cylindrical surfaces centered at the intake port. If the flow is constant through each cylinder, water velocity must increase as it gets closer to the port. This increase in velocity tends to agitate the gravel filter and the surrounding geological formation to such a degree that poorly cemented particles such as sand, silt and grit are dislodged and become suspended in the flow. This abrasive flow causes removal of material from the geological formation provoking the creation of caves which can collapse and damage part or all of the well and its equipment. In addition, the high velocity flow near the intake port erodes the casing. As the abrasive water travels up the tube, it erodes the impellers, the bearings, the shaft and other pump elements. The end result is regular costly maintenance to replace worn structures and a reduction in the useful lifetime of the well.
Another hydrodynamic result of pumping is a drop in the phreatic water level in the region surrounding the well. The normally flat water table takes on a shape closely resembling an inverted cone 19 whose central axis coincides with the axis of the well. This forms what is called the dynamic or pumping level 20 which is significantly below the original natural water level. Since the gravel is more permeable than the surrounding geologic formation, water tends to flow through the gravel rather than the formation. Hence, water removed by the pump tends to be replaced most quickly from above rather than laterally.
The drop of the phreatic level becoming the dynamic level lowers the pumping depth and exacerbates the problems of reduced efficiency. First, the well may have to be dug deeper to accommodate the drop in phreatic level since the intake port must be situated below the lowest depth the dynamic level will attain. Second, this causes a proportional increase in the amount of energy necessary to pump out a given amount of water. This reduces well efficiency and can even reduce the output of the well over a given time. Lastly, the speed of the water entering the well just below the dynamic water level creates additional turbulence which removes particles and minerals causing greater erosion of the casing and reducing the lifetime of the well.
Another common problem with aquifers is that part of the geological formation may contain contaminants such as salt or other minerals.
It is desirable therefore to have a pump which reduces the depth of the dynamic pumping level, reduces the amount of suspended solids in the water, and can select which aquiferous layers are to be exploited.